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Electronic cigarette use and indoor air quality in a natural setting
  1. Eric K Soule,
  2. Sarah F Maloney,
  3. Tory R Spindle,
  4. Alyssa K Rudy,
  5. Marzena M Hiler,
  6. Caroline O Cobb
  1. Department of Psychology, Virginia Commonwealth University, Center for the Study of Tobacco Products, Richmond, Virginia, USA
  1. Correspondence to Dr Eric K Soule, Virginia Commonwealth University, Department of Psychology, Center for the Study of Tobacco Products, P.O. Box 980205, Richmond, VA 23298-0205, USA; eksoule{at}


Introduction Secondhand smoke (SHS) from combustible cigarettes causes numerous diseases. Policies have been developed to prevent SHS exposure from indoor cigarette use to reduce health risks to non-smokers. However, fewer policies have been implemented to deter electronic cigarette (ECIG) use indoors, and limited research has examined the impact of secondhand exposure to ECIG aerosol.

Methods Indoor air quality was measured at a 2-day ECIG event held in a large room at a hotel. Fine particulate matter (PM) was measured using 2 devices that measured concentrations of PM 2.5 μm aerodynamic diameter or smaller (PM2.5). Measurements were taken before the event, over 2 days when the event was ongoing, and the day after the event. PM2.5 measurements were also taken from the restaurant at the hotel hosting the event and a restaurant at a nearby hotel.

Results During 6 time points when the event was ongoing, between 59 and 86 active ECIG users were present in the event room (room volume=4023 m3). While the event was ongoing, median PM2.5 concentrations in the event room increased from a baseline of 1.92–3.20 μg/m3 to concentrations that ranged from 311.68 μg/m3 (IQR 253.44–411.84 μg/m3) to 818.88 μg/m3 (IQR 760.64–975.04 μg/m3).

Conclusions PM2.5 concentrations observed at the ECIG event were higher than concentrations reported previously in hookah cafés and bars that allow cigarette smoking. This study indicates that indoor ECIG use exposes non-users to secondhand ECIG aerosol. Regulatory bodies should consider establishing policies that prohibit ECIG use anywhere combustible cigarette use is prohibited.

  • Electronic nicotine delivery devices
  • Public policy
  • Secondhand smoke

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Exposure to secondhand smoke (SHS) from tobacco cigarettes (mainstream smoke exhaled by smokers and sidestream smoke emitted from the end of a burning cigarette) is known to cause a wide range of diseases including coronary heart disease and cancers.1 ,2 To prevent non-smokers’ risk of negative health consequences associated with SHS from tobacco cigarettes, over 4400 municipalities in the USA have enacted laws that restrict cigarette smoking, including approximately 800 municipalities that require all restaurants and bars to be 100% smoke free.3 More broadly, approximately 92 nations have enacted some type of 100% smoke-free law.4 As electronic cigarettes (ECIGs) continue to grow in popularity among adolescents5 ,6 and adults,7 ,8 there is an increase in policies addressing exposure to secondhand ECIG aerosol. As of 2 October 2015, five US states and over 400 counties have implemented some form of restriction of ECIG use indoors.9 International policies are more varied with certain restrictions for ECIG use in UK airports and trains10 and reports of complete ECIG bans in indoor public places for Malta, Belgium and Spain.11

ECIGs are devices that use a heater to aerosolise a liquid often containing nicotine, propylene glycol, vegetable glycerin and flavourants. Research reveals that the aerosol produced from ECIG use contains toxicants including nicotine, glycols, aldehydes, metals, volatile organic compounds and polycyclic aromatic hydrocarbons.12 In addition, a growing body of work has examined the extent to which ECIG aerosol produced in ‘exposure chambers’ under controlled conditions by a single ECIG user13–15 or in private homes16 influences indoor air quality. However, to our knowledge, no published studies have examined the extent to which ECIG aerosol production under natural use conditions in public venues influences indoor air quality. Addressing this issue may provide critical information to policymakers interested in protecting non-ECIG users from involuntary inhalation of ECIG aerosols. The purpose of this study was to examine the effect of ECIG use on indoor air quality in a natural setting.


A research team attended an ECIG event (summer, 2015) held in a hotel meeting room over 2 days. ECIG use was permitted in all hotel areas. Indoor air quality (particulate matter measuring <2.5 μm (PM2.5)) was measured using two concealed TSI (Shoreview, Minnesota, USA) Sidepak AM510 Personal Aerosol Monitors in (1) the event room, (2) an indoor restaurant within the event hotel and (3) an indoor restaurant located at an adjacent hotel not hosting an ECIG event. The Sidepak AM510 measures PM by drawing ambient air into the device and analysing scattering light. This method has been used and validated previously for measuring secondhand tobacco smoke.17–21 (see also ref 15 and 22). PM2.5 was measured because it is a clinically relevant measure: particulates of this size are small enough to be deposited deep inside of the lung if inhaled and take longer to be removed by the body.23 The ease of concealment and ability to collect ambient air quality measurements in a natural environment make the Sidepak AM510 an appropriate choice for this type of assessment; however, this device cannot detect particle sizes below 100 nm in diameter. Because ECIG aerosol contains particles in this size range,14 the PM2.5 concentrations measured by the Sidepak AM510 likely underestimate the actual exposures being delivered to bystanders. However, using this device represented an appropriate option for the purpose of this study. Air quality measurements were collected in the event room the day before the event occurred, during the 2 days of the event at least two time points on each day, and the day after the event. Dimensions of each room where air quality was assessed were measured using a laser device, and these data were used to calculate room volume.

Prior to entering the venues, each Sidepak device was zero-calibrated according to device guidelines. Using methods similar to those reported elsewhere,22 a research team carrying a Sidepak device entered the venues and collected measurements for at least 30 min. While in the venues, researchers sat at a table with the device at table height or walked around the rooms to collect air quality readings throughout the venue. Immediately prior to and after each measurement session, 5 min of control measurements were collected by sampling outdoor air or in a room with no active ECIG use. The total number of individuals and the number of active ECIG users in the venues were counted at multiple time points during each session and a session count average was calculated.

The Sidepak was set to average 60 consecutive 1 s measurements of PM2.5 (1 min log interval). The first and last readings of each session were omitted in analyses to prevent including air from outside of the venue while entering or exiting. PM2.5 readings measured during each session were ordered and averaged to obtain median and mean concentrations of PM2.5 in the venue ambient air. A calibration factor was applied to these readings to generate a more accurate value for the concentrations of the PM2.5. Previous research of ECIG aerosol has used a calibration factor of 0.3215 that has been identified for cigarette SHS.18 ,19 ,24 Because the ECIG aerosol particle size profile includes particles with diameters below 100 nm,14 this calibration factor may underestimate PM2.5 concentration. However, in absence of an accepted calibration factor for ECIG aerosol, the cigarette SHS calibration factor was used. Additionally, active ECIG user density (defined as a visible ECIG in an individual's hand or mouth) was determined by calculating the number of ECIG users per 100 m3 in each venue. This determination was not possible during the event days because of the large number of individuals in the event room and size of the room (inability to reliably determine ECIG use in hand or mouth). Thus, all individuals in the main event room during the event days were considered active ECIG users for the purposes of calculating active ECIG density.


As displayed in table 1, the event room was a large space (4023 m3) compared with the hotel restaurants that were included in the study (596 and 942 m3). Cigarette smoking was not allowed inside any of the included venues; however, ECIG use was observed in the main ECIG event room (before, during and after the event) and the restaurant in the hotel hosting the event. During the event, 59–86 active ECIG users were observed at six different time points.

Table 1

Descriptive statistics and PM2.5 concentration for venues measured at different time points

Table 1 shows that the day before the event the median and mean PM2.5 concentrations in the main ECIG event room were less than 5 μg/m3 and both devices measured within 2 μg/m3 between device 1 (median=1.92 μg/m3, mean=2.08 μg/m3) and device 2 (median=3.20 μg/m3, mean=3.19 μg/m3). These control readings were of the same magnitude as the samples from the hotel restaurants (median=1.60–5.76 μg/m3, mean=1.72–5.89 μg/m3). When the event was ongoing, median PM2.5 concentrations in the event room ranged from 311.68 μg/m3 (IQR 253.44–411.84 μg/m3, mean=330.97 μg/m3, SD=88.18) to 818.88 μg/m3 (IQR 760.64–975.04 μg/m3, mean=869.12 μg/m3, SD=139.29; see table 1) with average median concentrations of 595.31 μg/m3 (average mean concentration=607.12 μg/m3) over the six time points measured. Approximately 17 h after the ECIG event concluded, the median PM2.5 concentration in the event room was 12.80–15.52 μg/m3 (mean 12.85–15.82 μg/m3) across both devices.

Figure 1 displays 1 min average PM2.5 concentrations in the event room pre-event (device 2), during day 1 of the event (device 1) and post-event (device 1).

Figure 1

Representative particulate matter measuring <2.5 μm (PM2.5) concentrations in ECIG event room measured before the event (pre-event), during the event (event day 1) and after the event (post-event). Each of these representative measurement sessions includes 5 baseline readings outside of event room, 30 readings in the event room and 5 endlog readings outside of event room.


In this study, the presence of fine PM increased dramatically—125–330 times higher—in a room where active ECIG use was occurring relative to the same room when no active ECIG use was occurring or in other venues where no active ECIG use was occurring. This observation indicates that indoor ECIG use can generate fine PM in high concentrations during natural use conditions in indoor environments. The PM2.5 concentrations observed in this study were approximately four times higher than PM2.5 generated by single ECIG users who used their device twice for 5 min in an exposure chamber (151.7 μg/m312) and more than 60 times higher than median PM2.5 measured inside the home of an ECIG user. 16 Particulate concentrations observed in this study were greater than PM2.5 concentrations found in hookah cafés and indoor bars that allow cigarette smoking (eg, mean PM2.5 concentrations from 17 hookah cafés of 369–384 μg/m3 and from bars that allowed cigarette smoking of 119 μg/m322). Additionally, the PM2.5 concentrations from this study are likely higher still compared with those reported previously22 because the PM2.5 concentrations reported in this study may underestimate the actual PM2.5 concentrations due to device measurement limitations and applying a calibration factor used to examine SHS from combustible cigarettes.

While ECIG aerosol often contains some of the same chemicals found in combustible cigarette or hookah smoke such as nicotine, the composition (ie, concentration of each chemical per puff or product use) of the PM measured in this study likely differs from PM generated from combustible cigarette and hookah smoking.14 ,15 ,25 Therefore, this study does not provide the data needed for a direct comparison of the harms associated with exposure to high concentrations of PM generated from ECIG use and hookah or combustible cigarette smoke. While the exact harm potential of secondhand exposure to ECIG aerosol is not currently known, the fact that secondhand ECIG aerosol contains fine particulates, nicotine, carcinogenic aldehydes, polycyclic aromatic hydrocarbons and volatile organic compounds13–16 indicates that exposure to secondhand ECIG aerosol may present some degree of harm to bystanders. Importantly, any of these bystanders who are not ECIG users have opted not to inhale ECIG aerosols yet, should they share indoor space with an ECIG user who is using their ECIG actively, are involuntarily inhaling these fine particulates.

This study is the first to examine ECIG-generated PM in a natural public setting. While the venue examined in this study may differ from some places where ECIGs are used indoors commonly, we expect that PM2.5 concentrations measured in other venues, such as bars or restaurants that allow ECIG use, would be elevated similarly compared with the concentrations reported in this study, again requiring non-users to inhale fine PM involuntarily. This involuntary inhalation unfortunately could be the norm if policies are not established that prevent ECIG use in airplanes, hotels, hospitals, schools, restaurants, bars and other venues were cigarette smoking was once commonplace in this country. Policymakers may want to consider to what extent ECIG users, like cigarette smokers, are required to comply with all existing clean indoor air regulations.

What this paper adds

  • This is the first study to examine the effect of electronic cigarette (ECIG) use on indoor air quality in a natural setting. Particulate matter (PM) measuring <2.5 μm concentrations in a large room with active ECIG users were higher than those previously reported in hookah cafés and bars that allow cigarette smoking. While the harm potential of secondhand exposure to ECIG exposure among non-ECIG users is unknown currently, these data indicate that indoor ECIG can affect indoor air quality. Policies that prohibit indoor ECIG use would prevent non-ECIG users’ non-voluntary inhalation of ECIG-generated PM.


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  • Contributors EKS and COC made significant contributions to the study design, data analysis and writing of the manuscript. SFM, TRS, AKR, MMH and COC conducted all data collection and provided critical review of the manuscript. All authors approved the final version of the manuscript.

  • Funding Research reported in this publication was supported by the National Institute on Drug Abuse of the National Institutes of Health under Award Number P50DA036105 and the Center for Tobacco Products of the US Food and Drug Administration.

  • Disclaimer The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health or the Food and Drug Administration.

  • Competing interests None declared.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Data sharing statement This manuscript contains all data collected for this study. Data are available by email request from the corresponding author (EKS).